What are teses tiny rust-like stains?

[poolbee]

It was the builder that added the salt. They told me I'd probably see these little satins and not to worry about them. My steps now have a large amountof these little specks all over them.
What should I use to get the metals out? I saw Jack's Blue stuff-I have a SWG and a heater, the purple stuff is not for heaters as I recall. Is there a better formula out there and what is the proper way to do it? I really don't trust the pool stores to know.
one other thing-when trying the vit. C does the strength matter? I used 250 mg. tabs and results were OK, but better than with cal hypo. Do I need stronger tabs?